Processes for the deacidification of liquids, especially water



Patented Apr. 18, 1939 UNITED STATES PATENT OFFICE PROCESSES FOR THEDEACIDIFICATION OF LIQUIDS, ESPECIALLY WATER No Drawing. ApplicationJuly 24, 1936, Serial No. 92,464. In Germany July 27, 1935 13 Claims.(01. 210-23) In the purification of water for household and industrialpurposes, especially for boiler feed purposes, numerous processes havebeen suggested, which rest partially on chemical precipitation oradsorption of substances dissolved in water, or which remove especiallythe hardness from the water by base exchange. In base exchange, anotherbase is substituted for that originally present; there is no subtractionof solids.

these processes have the fault that the resultant waters contain more orless large quantities of alkali salts. usually sodium salts, which areformed by conversion in the diiferent processes from the earth alkalisalts, in other words from the hardness of the water. To this there arestill in addition those alkali salt quantities which are contained innearly all waters in addition to the hardness causing salts, and whichare removed by none of the above mentioned processes.

39 Hard waters usually contain "permanent hardness (caused by sulfatesor chlorides) as well as temporary hardness (carbonate hardness).

By hydrogen exchange zeolites, the bases or cations of the carbonatescan be readily re- 95 moved, leaving CO2 which can be readily removedfrom the water. But the cations of the sulfates and chlorides whenremoved leave free mineral acids, sulfuric and hydrochloric. In treatingordinary water containing both kinds of hardness, the effluent watercontains free CO2 derived from the carbonate hardness and free mineralacid derived from the sulphate or noncarbonate hardness. The freemineral acid imparts methyl orange acidity to the water, a pHsubstantially less than 7. While the free CO2 can now be removed withoutdifilculty, for instance, by aeration, evacuation, heating or the like,this is not the case with regard to the mineral acids, as they areeither not volatile at all P or, as a result of their dilution, even ifthey are volatile, cannot be expelled. Since however water containingmineral acids as such can be utilized only in the rarest cases,especially not for boiler feed purposes, one was compelled to neutralize46 the mineral acids again, or rather to arrange the exchange reactionin such a way that a neutralization of the mineral acids took placeduring the exchange reaction itself. In all these cases a quantity ofsalts at least corresponding 60 to the sulphate hardness was now againadded to the water. Removal of sulphuric acid can be eflected byprecipitating it with bases which form not easily soluble salts with it,or with salts of such bases the anion of which is easily removed,

55 like, for instance, barium hydroxide or barium All carbonate. But theprocedure, particularly with the use of, barium carbonate, is acomparatively slow and incomplete one. Besides, the very fineprecipitate needs a fairly long period to settle and finally there arealso dosing difllculties, as 5 precisely equivalent amounts must beused, entirely disregarding the fact that in the use of bariumcarbonate, barium carbonate always enters the liquid also by trickling.Barium carbonate is not wholly insoluble. Finally, hydro- 10 chloricacid cannot be removed at all in this manner. My copending applicationSerial No. 10,127, filed March 8, 1935, discloses processes abstractingthe bases of salts dissolved in water. leaving mineral acids in thewater.

In accordance with the present invention, waters which are salt free orsalt poor are obtained by a double treatment; the base being firstexchanged for a hydrogen ion and then the acid water brought intocontact with such substances that are capable of retaining the acids,without on their part giving off to the water objectionableconstituents. As such substances the oxides or hydroxides of such metalsthat are capable of forming insoluble basic compounds, like, forinstance, the oxides or hydroxides of iron, aluminum, zinc, tin, etc.,which are physiologically harmless have proved especially desirable. Inthemselves other metal oxides or hydroxides as for instance thecorresponding compounds of copper, lead and others can be used with thesame or similar effects.

The process may be carried out in various ways. The acid water resultingfrom an abstraction of bases can be mixed with an excess of, forinstance, iron hydroxide paste, which has been produced by precipitationwith alkaline substances at an elevated temperature or cold from ferricsalts, and separated by filtration in order to obtain a'neutral water,which still contains only 40 very small quantities of salt and isremarkably similar to distilled water. This similarity is even greaterbecause by the desilicifying action of the iron hydroxide, SiO-z is alsonearly completely removed from the water.

Another form of carrying out the process may consist in drying thepressed and preferably washed hydroxides of the metals, in connectionwith which the drying is carried only to such an extent that not all thewater of constitution is expelled. The resultant substances, which forinstance still contain 10 per cent to 20 per cent water removable byignition, are crushed to a suitable grain size and the acid water ispercolated through a pervious bed of the granules.

The filtration can be carried out cold, as well as warm. but the effectseems to be better at a low temperature.

A further form of theprocess consistsiniettlng the acid water itselfflow over metals, preferably with large surface area, or in bringing itin contact with them in other, ways, in connection with which, when ametal is involved which has two valences, like, for instance, iron, onemust take care that the higher oxidation step is at least completed inthe eiliuent water by suitable addition of air or other oxidationagents, for instance, permanganate or permanganic acid, .pyrolusite orpersulphuric acid and its salts and conversion products, like hydrogenperoxide or also ozone, chlorine, etc., or anodic oxidation. In otherwords, in this method of execution the formation of the oxides orhydroxides takes place from the metals themselves. In this connectionone can apply all the measures which will serve to accelerate theformation of hydroxides. In place of the pure metals, metal alloys canbe used, for instance, those of zinc and aluminum,

or by using several metals which are mixed with each other, one canproduce galvanic couples for instance within the metal filters, forinstance, copper and iron.

One can also use naturally occurring substances, which have theseproperties, for instance, bauxite, pyrolusite or bog iron ore or alsosiderite. In using the last named, an after-treatment with oxidizingagents, as mentioned above, is necessary, in order to form tri-valentiron from the di-valent iron. If the free CO: is not previously removed,the ferrous carbonate is also attacked by it and ferrous iron from thissource must also be converted into the ferric form by the oxidizingagent.

If the oxidation of the iron does not take place or takes place onlyvery slowly or incompletely because of too high hydrogen ionconcentration (about neutral point) the water is given a smallerhydrogen ion concentration by addition of very small quantities ofalkali, in other words, is made slightly alkaline, whereupon then theoxidation, for instance, also with air takes place rapidly.

If stronger salt solutions are present like, for instance, in sea water,it is generally not possible to obtain a removal of salt with a singletreatment with a hydrogen ion exchange material and one acid absorbent.In order to arrive at a satisfactory result in this connection, thesolution must be passed through a system in which hydrogen exchangematerial and acid absorbent alternate so often, for instance three toten times or more, that the desired result of partial or completefreedom from salt is achieved. In this con-' nection the series in whichthe individual pairs of hydrogen exchange material and acid absorbentsare arranged can be altered, so that the latter pairs may be first, etc.

In general it may be said that the regeneration of the hydrogen ionexchange material must usually be more frequent than that of the acidabsorbents. when in using the latter one works with substances which areworth while regenerating in view of their high cost or in view of theeffort required in their production.

As already mentioned above, in this treatment of the acid water not onlya removal of the acid by binding, but also a removal of the SiO: byabsorption takes place. The fact that in this treatment with metaloxides or hydroxides other impurities of the water, like humussubstances. insofar as they have not been removed previsalts.

ously, are also removed. should be stressed particularly.

It is desirable to use a water for the ion exchange, from which the 8102has been previously removed, for instance a water that has been treatedwith suitable magnesium compounds or metal oxides or hydroxides or gels.Likewise the water can be treated previous to the ion exchange withother softening agents which bring about a partial softening, while theresidual hardness is then removed by ion exchange. In all theseprocesses, however, care must be exercised that only as small a quanttiyas possible of alkali salts enter the water.

The procws relates not only to water which contains hardness but also towaters which contain other salts, for instance, alkali salts, possiblybesides the hardness; in other words, generally speaking to dilute saltsolutions which contain salts of the mineral acids or other acidsbesides, for instance, carbonates or bicarbonates.

The regeneration of the exchange material may be effected with acids,while the metal compounds, insofar as the regeneration is worth whilemay be regenerated with alkaline solutions, for instance, ammonia,caustic soda, sodium carbonate, etc., whereby the basic compounds arereconverted into the hydroxides. The regeneration has the effect ofcharging the basic compounds with hydroxyl ions replacing the acidanions removed from the water.

For example, a water containing a total hardness of 187 parts permillion as CzCOa of which 135 p. p. m. was carbonate hardness and 52 p.p. m. non-carbonate hardness, besides so much alkali salt as isequivalent to the hardness of approximately 53 p. p. m. and in addition16 p. p. m. SlOz was treated in accordance with the invention.

It first passed through a carbon containing base abstracting material,regenerated with hypo-, chloric acid, and thereupon through a dried,finely granulated iron oxide gel. And in this connection two parts byvolume of the base abstracting material and one part by volume of theiron oxide gel were used, through which 200 parts by volume of the waterwere passed at a velocity of 1. e. also parts by volume, had an averagecomposition of 70 p. p. m. NazSOs and 5.2 p. p. m. $102. All of thewater was free from hardness.

The example shows that in the first half of the water nearly all of thesalt contained as alkali salt in the raw water was removed, while in thesecond half the salt content corresponds to that of the alkali salts inthe raw water.

Not only aqueous solutions can be subjected to this treatment but alsosolutions of substances which in themselves are inactive in the sense ofion exchange, like for instance sugar solutions, which are to be freedof the salt content of lime salts or alkali salts. As is shown, thecrystallization of sugar is retarded considerably by these Thisdifliculty is eliminated by the above described process, since sugarsolutions are obtained which are completely or nearly completely free ofsalt.

As will be noted, in the present invention, salines can be subtractedfrom water by a 2-step operation: the cation of the saline being takenup by a hydrogen zeolite leaving the anion in solution and this latterremoved by contact with extensive surfaces of a metal oxide.

What is claimed is:-

l. The process for removing salts from industrial water, especiallyboiler feed water, which comprises filtering the saline water through ahydrogen exchange material and then filtering the acid filtrate througha metal oxide gel charged with hydroxyl ions by treatment of the gelwith alkali.

2. A process of purifying hard water containing saline impurities whichcomprises first treating the water with a hydrogen exchange materialexchanging saline cations in the water for hydrogen, thereby leavingfree mineral acid in the Water, and subsequently abstracting said acidfrom the water by treatment with an oxide adapted to retain said acid ininsoluble form.

3. In the process of claim 2, abstracting free acid by contacting theacid water with a preformed metal oxide.

4. In the process of claim 2, abstracting free acid by passing the acidwater through a granular bed of dried hydrated metal oxide gel.

5. In the process of claim 2, abstracting free acid by passing the acidwater through a bed of hydrated ferric oxide granular dried gel.

6. A process of purifying water containing dissolved salts whichcomprises exchanging cations of the salts for hydrogen by contacting thewater with a hydrogen-ion zeolite leaving in the water the anions of thesalts as free acid and thereafter removing said free acid from the waterby contacting it with extensive surfaces of granular dried metal oxidegel abstracting the acid.

'7. In the process of claim 6, regenerating the hydrogen-ion zeolite forreuse by a dilute acid wash and regenerating the metal oxide gel forreuse by a dilute alkali wash.

8. In softening water containing permanent hardness by aid of a hydrogenzeolite abstracting bases therefrom and leaving the water containingresidual mineral acid, a process of coning the water with a hydrogenexchange material exchanging saline cations in the water for hydrogen,thereby leaving free mineral acid'in the water, and subsequentlyabstracting said acid from the water by passing the acid water through abed of dried granular hydrated ferric oxide gel.

11. A process of purifying hard water containing saline impurities whichcomprises first treating the water with a hydrogen exchange materialexchanging saline cations in the water for hydrogen, thereby leavingfree mineral acid in the water, and subsequently abstracting said acidfrom the water. by passing the acid water through a pervious bed ofdried granular partially dehydrated aluminum hydroxide in gel form.

12. The process for removing salts from industrial water, especiallyboiler feed water, which comprises filtering the saline water through abase-exchanger containing hydrogen ions and then filtering the acidfiltrate through a granular iron oxide gel charged with hydroxyl ions bytreatment of the gel with alkali.

13. The process for removing salts from industrial water, especiallyboiler feed water, which comprises filtering the saline water through acarbonaceous hydrogen zeolite, and then filtering the acid filtratethrough a granular iron oxide gel charged with hydroxyl ions bytreatment of the gel with alkali.

CERTIFICATE OF CORRECTION,-

Patent No. 2,155,518

A ril 18, 1959- It is hereby certified that error appears in the printedspecification of the above numbered patent requiring correction asfollows: Page 2, second coltmm, line 15, for "quanttiy" read quantity;line 55, for 60 read CaGO line L l-b2, for hypochloric readhydrochloric; line 1+9, for "filler" read filter; and that the saidLetters Patent should be read with this cor-- rection therein that thesame may conform to the record of the case in the Patent Office.

Signed and sealed this. 6th day of June, A. D. 1939.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

